1. Field of the Invention
This invention relates to radial pneumatic tires used for vehicles, and more particular to the design of the lower sidewall and bead area of a run-flat tire to reduce the effort in mounting the tire on a standard rim and to improve the retention of the tire on the standard rim during a loss of inflation pressure.
2. Description of the Art
The need to carry a spare tire in a vehicle to replace a flat tire, or more basically the need for a vehicle operator to stop and replace a deflated tire at an inconvenient location, has long been a concern of the vehicle operator. Many of these concerns can be addressed with the use of a run-flat tire for allowing the operator to reach a safe place or a service station before replacing a tire which has lost its inflation pressure.
One of the problems associated with providing a run-flat tire is to maintain acceptable performance of the run-flat tire upon deflation. Essential to solving this problem is to provide a run-flat tire which stays on the rim and keeps the vehicle supported so the vehicle may drive to a more convenient location to repair or replace the tire. The tire is generally retained on the rim by the inflation pressure in the tire during normal running of the vehicle. Absence of this inflation pressure tends to cause the tire to want to be disconnected from the rim. This is especially true during lateral maneuvers of the vehicle. Solutions to this rim unseating problem include providing a special rim having a hump or a depression for engaging the run-flat tire having a corresponding special bead design. Typical efforts to modify the tire/rim seat interface profiles are disclosed in U.S. Pat. Nos. 4,779,658; 5,263,526; and 5,427,166. However, the use of standard rims with these special run-flat tires will not optimize the bead unseating problem. In addition, the effort required to seat these special run-flat tires on rims with special tire/rim interface designs is excessive.
Part of the rim unseating and vehicle handling problems have been solved by the use of sidewall reinforcing members in a run-flat tire to provide laterally stiffened sidewalls. Typical run-flat tires with reinforced sidewalls are disclosed in the three U.S. Patents disclosed above as well as in U.S. Pat. Nos. 5,158,627; 5,368,082; and 5,511,599. The crescent shaped sidewall reinforcing members are essential for holding the tread displaced from the rim to make the tire respond to vehicle maneuvers with the loss of inflation pressure in the run-flat tire. Tires with sidewall reinforcing members are used with the improved bead seat design of this invention.
The heavy duty radial tire of U.S. Pat. No. 5,085,260 discloses a smaller apex filler along with a number of carcass layers turned up around the bead core. The length of carcass turn-up portions and the position of the bead core in relation to the rim flange height is used to obtain bead strength. Accuracy in the placement of end points of each carcass layer is important in the teachings of this 1992 patent.
Changing the shape, dimensions and material properties of components in the lower sidewall and bead of a tire can affect their ability to resist higher forces and moments. The run-flat tire can be designed to take advantage of changing shape, dimensions and material properties. One component which can be easily modified is the bead filler. A bead filler which has been extended radially into the area of the sidewall in U.S. Pat. Nos. 4,640,329; 4,766,940; and 5,048,584. This extension provides improved transverse and radial load supporting capabilities for the tire. However, the material properties of the filler needs to be different near the bead core than radially outward in the sidewall to resist different loads in these different locations of the run-flat tire and to facilitate an efficient tire fabrication process. The disclosures of U.S. Pat. Nos. 4,046,183; 4,120,338; and 4,508,153 and Japan Patent No. 5-178037 illustrate the use of bead fillers having two parts; being one part adjacent a bead core and another part extending into the sidewall area. These two-part bead fillers use different size, shape and material properties for each of the two parts. The bead fillers of these references also require additional reinforcing layers placed adjacent to the bead fillers to improve durability and strength of the bead region of the tire. The need remains to simplify the use of two-part bead fillers while maintaining their advantages.
Another design parameter which can be incorporated to transfer loads from the vehicle to the ground by way of the run-flat tire is the use of the rim flange. If a tire can be made to contact the flange of the rim, the vehicle loads can transfer loads to the rim at its flange. The rim flange contact is also useful in transferring lateral loads between the tire and the rim that would otherwise act to unseat the tire from the rim. Rim flange seating of the tire is well known in the art as disclosed in U.S. Pat. Nos. 3,983,918; 4,203,481; and 5,033,524. Both U.S. Pat. Nos. 3,983,918 and 5,033,524 disclose the use of an additional product in the tire to interface with the rim flange. A gap between the rim and a buttress on the tire in U.S. Pat. No. 3,983,918 is closed when the buttress contacts the rim flange. The tire to rim flange contact is known to help with vehicle handling in some maneuvers of the vehicle and to degrade the vehicle handling with other maneuvers. It is important to know at what operating condition the tire to rim flange can be used as an advantage. The need remains to identify when contact of a run-flat tire with a rim flange can be useful for the partially inflated run-flat tire.
A further problem exists with the pressure of the run-flat tire on the rim seat portion of the tire to rim interface. A tire is mounted on a rim with a combination of inflating and pushing the tire to its proper place on the rim. The rubber in contact with the rim must be durable and effective in sealing the interface against loss of inflation pressure caused by air leaking out from inside the tire. It is well known in the art to use an additional rubber layer for making direct contact with the rim seat portion. In U.S. Pat. No. 5,511,599 a rim seat ply is used to making contact with a rim. Economy in manufacturing the run-flat tire can be realized by a single bead interface rubber. The use of a single rubber component for the bead interface rubber is disclosed in U.S. Pat. Nos. 4,235,273; 4,790,364; and 5,033,524. The profile of the innermost area of the bead interface rubber is also important for providing desired pressures at the tire to rim interface. In U.S. Pat. Nos. 4,554,960 and 5,464,051 a profile is disclosed for providing a proper bead to rim interface seat area. The extent of a single bead interface rubber which can also provide a rim flange seat and a durable bead toe remains unsolved by these references. The material properties of this bead interface rubber also remains undefined.
Even with the improvements of the references the need remains to have a lower sidewall and bead structure which has an improved bead retention capability without compromising the ability to sustain the same vehicle loads and without the necessity of added reinforcing layers or other non-standard tire components. A coexisting need is to be able to use run-flat tires on standard rims that generally exist in the replacement market at the present time. Both of these needs should be achieved while maintaining a manufacturing process with limited changes and preferably lower costs for the run-flat tire.
Accordingly, one object of this invention is to provide a run-flat tire having annular beads designed so that the run-flat tire can be easily mounted on a standard rim of a vehicle without excessive over-pressures.
Another object of the present invention is to provide a run-flat tire having annular beads designed to maintain a good seal between the tire and the rim for maintaining an inflation pressure within the tire.
Yet another object of the present invention is to provide a run-flat tire having annular beads designed so that the run-flat tire strongly resists being removed from the standard rim during loss of inflation pressure.
A further object of the present invention is to simplify the design of the bead area to reduce the number of different rubber components used in the bead area when manufacturing the run-flat tire.
Still another object of the present invention is to use materials in the bead area which are resistant to damage when mounting the run-flat tire on the standard rim and resistant to loss of air between the tire and the rim during normal operation of the run-flat tire on the vehicle.